An introduction to making biochar

John Hermans explains what biochar is, its environmental benefits and the process he uses to make it.

It was not until I read The Biochar Revolution by Paul Taylor that I began to think about biochar’s agricultural and environmental value, and decided to make the effort to make biochar at home. This article won’t attempt to summarise the book but rather focus on how I’ve used its approach to benefit our household.

What is biochar?

In a word, biochar is charcoal. Crushed into small particles, the charcoal can be used to improve the nutrient- and water-holding capacity of soil, and so improve plant growth and productivity.

Biochar is a relatively new word, but biochar’s use has been documented as far back as the Amazonian Indians, who created tera preta or ‘black earth’. These nutrient-enriched soils retain much of their higher fertility, and their char, thousands of years after they were created.

Biochar can also permanently lock up carbon to help neutralise our carbon footprint. In this world where governments are largely failing to mitigate a climate catastrophe, this is another path for a ‘bottom-up’ global effort.

Why make biochar?

Biochar is now commercially available as a soil conditioner, at around $10/kg, but if you are not confined by allotment size, it is quite easy and cheap to make instead. You can also then control what goes into it.

In my case, I have been using the sticks and leaves that I would otherwise have burnt to reduce summer bushfire risk.
Making it has also given our household another option for becoming truly carbon neutral, other than planting trees. Biochar means we can now lock up atmospheric carbon in the soil, potentially for thousands of years, rather than have it re-enter the atmosphere when the ground litter rots or is burnt. Once it is added to the soil, it remains mostly inert to oxidation and hence does not re-enter the carbon cycle. At the same time, it increases the soil fertility in our extensive food garden.

Biochar chemistry

When organic matter is burnt in the open air, it nearly all burns to ash, with only very small amounts of unburnt black char. It is possible to make char in a controlled open-air fire by extinguishing it early with water, but smoke, heat, flames and gas emissions will result.

In biochar manufacture it is preferable to use enclosed steel drums to control oxygen delivery and to burn most, if not all, of the carbon monoxide, hydrogen and methane which otherwise are given off in smoke. If unburnt, most of these gases have a far higher greenhouse gas effect than CO2. When the fuel is burnt in controlled conditions, they are converted to CO2. An added advantage is that it is a fairly smoke-free production process—far more neighbour-friendly than open-air fuel reduction burning.